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Protocols (ex: http, ftp, mailto) are different methods of sending information over the Internet. Protocols may be handled by Mozilla applications themselves, or they may be passed to external applications, or they may not be handled at all. On Linux and Mac systems, this preference determines what external program should handle the request.

Possible values and their effects

A path to a program to handle the request.


  • This preference has no effect on Windows, as the application to run is determined by the OS. See this article for details. [EDIT: on windows VISTA, setting network.protocol-handler.expose.http to true combined with the flashGot add-on, will allow you to select the program for opening a locally saved copy of the destination link.)
  • network.protocol-handler.expose-all or network.protocol-handler.expose.(protocol) (which tell the application that this protocol should be handled in some way) and network.protocol-handler.external.(protocol) (which tells the application that this protocol should be handled externally) must be set to true for this preference to take effect.
  • This preference only exists by default for certain protocols.
  • If the path doesn't refer to an executable program, the application will inform you "Protocol (protocol) isn't associated with any program"

First checked in

2002-03-26 by Patrick C. Beard

Has an effect in

  • Netscape (all versions since 7.0)
  • Mozilla Suite (all versions since 1.0)
  • Mozilla Firefox (all versions)
  • Seamonkey (all versions)

See also

Related bugs

Related preferences